diff --git a/man/machine-id.xml b/man/machine-id.xml
index d0bfbd240d..6ca9990988 100644
--- a/man/machine-id.xml
+++ b/man/machine-id.xml
@@ -55,10 +55,12 @@
Description
The /etc/machine-id file
- configures the unique machine id of the local system
- that is set during installation. It should contain a
- single newline-terminated, hexadecimal, lowercase 16
- character machine ID string.
+ contains the unique machine id of the local system
+ that is set during installation. The machine ID is a
+ single newline-terminated, hexadecimal, lowercase 32
+ character machine ID string. (When decoded from
+ hexadecimal this corresponds with a 16 byte/128 bit
+ string.)
The machine ID is usually generated from a
random source during system installation and stays
@@ -69,7 +71,7 @@
The machine ID does not change based on user
configuration, or when hardware is replaced.
- This machine id follows the same format and
+ This machine ID adheres to the same format and
logic as the D-Bus machine ID.
Programs may use this ID to identify the host
@@ -81,6 +83,35 @@
call POSIX specifies.
+
+ Relation to OSF UUIDs
+
+ Note that the machine ID historically is not an
+ OSF UUID as defined by RFC
+ 4122, nor a Microsoft GUID. Starting with
+ systemd v30 newly generated machine IDs however do
+ qualify as v4 UUIDs.
+
+ In order to maintain compatibility with existing
+ installations, an application requiring a UUID should
+ decode the machine ID, and then apply the following
+ operations to turn it into a valid OSF v4 UUID. With
+ id being an unsigned character
+ array:
+
+ /* Set UUID version to 4 --- truly random generation */
+id[6] = (id[6] & 0x0F) | 0x40;
+/* Set the UUID variant to DCE */
+id[8] = (id[8] & 0x3F) | 0x80;
+
+ (This code is inspired by
+ generate_random_uuid() of
+ drivers/char/random.c from the
+ kernel sources.)
+
+
+
History
@@ -88,7 +119,7 @@
/etc/machine-id originates in the
/var/lib/dbus/machine-id file
introduced by D-Bus. In fact this latter file might be a
- symlink to the
+ symlink to
/etc/machine-id.
diff --git a/src/machine-id-setup.c b/src/machine-id-setup.c
index 98e288e1b5..be51d0dec7 100644
--- a/src/machine-id-setup.c
+++ b/src/machine-id-setup.c
@@ -32,16 +32,28 @@
#include "util.h"
#include "log.h"
+static void make_v4_uuid(unsigned char *id) {
+ /* Stolen from generate_random_uuid() of drivers/char/random.c
+ * in the kernel sources */
+
+ /* Set UUID version to 4 --- truly random generation */
+ id[6] = (id[6] & 0x0F) | 0x40;
+
+ /* Set the UUID variant to DCE */
+ id[8] = (id[8] & 0x3F) | 0x80;
+}
+
static int generate(char id[34]) {
int fd;
- char buf[16];
- char *p, *q;
+ unsigned char buf[16], *p;
+ char *q;
ssize_t k;
assert(id);
/* First, try reading the D-Bus machine id, unless it is a symlink */
- if ((fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW)) >= 0) {
+ fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
+ if (fd >= 0) {
k = loop_read(fd, id, 33, false);
close_nointr_nofail(fd);
@@ -56,7 +68,8 @@ static int generate(char id[34]) {
}
/* If that didn't work, generate a random machine id */
- if ((fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
+ fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
+ if (fd < 0) {
log_error("Failed to open /dev/urandom: %m");
return -errno;
}
@@ -69,6 +82,11 @@ static int generate(char id[34]) {
return k < 0 ? (int) k : -EIO;
}
+ /* Turn this into a valid v4 UUID, to be nice. Note that we
+ * only guarantee this for newly generated UUIDs, not for
+ * pre-existing ones.*/
+ make_v4_uuid(buf);
+
for (p = buf, q = id; p < buf + sizeof(buf); p++, q += 2) {
q[0] = hexchar(*p >> 4);
q[1] = hexchar(*p & 15);
@@ -96,10 +114,12 @@ int machine_id_setup(void) {
* will be owned by root it doesn't matter much, but maybe
* people look. */
- if ((fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444)) >= 0)
+ fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
+ if (fd >= 0)
writable = true;
else {
- if ((fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
+ fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY);
+ if (fd < 0) {
umask(m);
log_error("Cannot open /etc/machine-id: %m");
return -errno;
@@ -126,7 +146,8 @@ int machine_id_setup(void) {
/* Hmm, so, the id currently stored is not useful, then let's
* generate one */
- if ((r = generate(id)) < 0)
+ r = generate(id);
+ if (r < 0)
goto finish;
if (S_ISREG(st.st_mode) && writable) {
@@ -146,7 +167,8 @@ int machine_id_setup(void) {
mkdir_p("/run/systemd", 0755);
- if ((r = write_one_line_file("/run/systemd/machine-id", id)) < 0) {
+ r = write_one_line_file("/run/systemd/machine-id", id);
+ if (r < 0) {
log_error("Cannot write /run/systemd/machine-id: %s", strerror(-r));
unlink("/run/systemd/machine-id");